I see nothing requiring two citizen parents in S. Res. 511.Whereas John Sidney McCain, III, was born to American citizens (plural!) on an American military base in the Panama Canal Zone in 1936: Now, therefore, be it
Resolved, That John Sidney McCain, III, is a `natural born Citizen' under Article II, Section 1, of the Constitution of the United States.
It says plural parents. It says that because that is the fact situation with Sen. McCain. It does not say anywhere that one American parent would not be sufficient. It also does not apply to Obama, since no one says he was born in the Canal Zone. If anyone wishes to read more into the resolution (which by the way is of doubtful legal validity anyway) more than the actual words say, that is their lookout.